The following discussion of the background to the invention is included to explain the context of the invention. This is not to be taken as an admission that any of the material referred to was published, known or part of the common general knowledge in Australia as at the priority date established by the present application.
It is frequently useful to detect and to determine the concentrations of various dissolved chemical substances present in varying concentrations in a flowing liquid stream such as, for example, the effluent of a high-performance liquid chromatograph. If such chemical substances absorb light of characteristic wavelengths they can be detected by spectrophotometry. It is convenient to pass the flowing liquid stream (or a representative portion thereof) through a flow through cell for continuous spectrophotometric measurements. To obtain good resolution of different chemical substances eluted from the column of a chromatograph it is important that the effluent stream should undergo as little mixing as possible in its passage through the flow through cell. This is favoured by keeping the volume of the cell small and by ensuring that all parts of the conduit or passage through the cell are efficiently swept by the flowing liquid. An example of a flow cell having such characteristics is disclosed by Berick and Magnussen, Jr. in U.S. Pat. No. 4,374,620 (Feb. 22, 1983). Another example is disclosed by Magnussen, Jr. in U.S. Pat. No. 5,064,287 (Nov. 12, 1991). In the flow cell of each of these disclosures, means are provided adjacent the entrance end of a flow through passage and surrounding that passage to modify the flow characteristics of a liquid entering the passage. Such means evenly distributes the flow circumferentially as it enters the passage to thereby reduce undesirable mixing of the flow. However both of these flow through cells are difficult to manufacture.